1. Field of the Invention
Exemplary embodiments of the present invention relate to a light guide unit for a point light source, a backlight assembly and a display device having the light guide unit. More particularly, exemplary embodiments of the present invention relate to a light guide unit for a point light source having an improved light efficiency, a backlight assembly and a display device having the same.
2. Description of the Related Art
Electronic devices such as a cellular phone, a digital camera, a notebook computer, a monitor and the like include a display device to display data into images. A liquid crystal display (LCD) device is widely used as the display device since the LCD device has merits such as a thin thickness and a light weight.
The LCD device includes a crystal and a backlight assembly for displaying images. The backlight assembly provides a light into a display panel in order to display the images using a small amount of light. The backlight assembly includes a light source and an optical unit for improving optical characteristics of a light emitted from the light source. Particularly, structure of the light source and the optical unit, and an arrangement relationship may have the most important influence on power consumption, lightening and the thinning of the LCD device. In order to reduce the power consumption, weight, thickness and volume of the LCD device, attempts to improve a structure of the backlight assembly has been continued.
The LCD device applied to the notebook computer or the monitor generally includes a cold cathode fluorescent lamp (CCFL) as a light source of the backlight assembly. However, the LCD device applied to a smaller device such as the cellular phone and the digital camera includes a point light source as a light source of the backlight assembly.
The point light source may include a light emitting diode (LED). The LED has power consumption, a weight, a thickness and a volume smaller than those of the CCFL. Hence, the LED is advantageous for a mobile or smaller display device. The LED may be disposed directly under a display section of a display pane, which is referred to a direct type. Alternatively, the LED may be disposed outside of the display section, which is referred to an edge type.
In a case of the direct type, the optical unit includes a diffusing plate that improves a luminance uniformity of a light emitted from the LED and a light-condensing sheet that improved a luminance of a front. In a case of the edge type, the optical unit includes a light guide plate, a diffusing sheet and a light-condensing sheet. The light guide plate may guide a light emitted from the LED into the display section. The diffusing sheet may diffuse a light exiting from the light guide plate. The light-condensing sheet may condense the light in a direction of a perpendicular of the display panel.
Several LEDs may be used for a mobile display device or a smaller display device. However, using one or two LEDs having a high illumination may be advantageous to reduce the power consumption, thickness and weight. When a single LED is used to the edge type, the LED is usually disposed on an edge of the light guide unit for an efficient diffuse of a light. Then, a light emitted from the LED may proceed in a direction of a diagonal line of the light guide unit and may be guided to the display panel disposed on the light guide unit.
When the backlight assembly includes two or more LEDs, the LEDs are disposed on a side surface of the light guide unit (referred to a light incident portion hereinafter). A portion having a highest luminance of the light guide unit is near the light incident portion. A luminance in a side portion of the display panel may be excessively high in the backlight assembly including the above-mentioned structure, so that a quality of a display may be deteriorated.
In order to improve uniformity of luminance, the light incident portion of the light guide unit is disposed apart by a predetermined interval from an outside of the display section of the display panel. As a result, the light guide unit has a rectangular shape having a longer side than that of the display section. The two or more LEDs are mounted on the light incident portion disposed outside of the display section.
A means to improve a use efficiency of a light emitted from the LED is related with respect to reduce the power consumption and improve the quality of the display.
An amount of a light incident through the light incident portion may be leaked out through a side surface connected to the light incident portion. Particularly, most of the light incident through the light incident portion may not be totally reflected but be leaked out through the side surface connected to the light incident portion because of an arrangement structure between the side surface and the light incident portion. A light leaked out may not be guided to the display section, so that the power consumption of the display device may be wasted and the quality of display may be deteriorated.